Metal halide gas-discharge lamps are commonly used in a number of venues such as sporting arenas and stadiums, plant nurseries, and industrial plants. Like other gas-discharge lamps, metal halide lamps produce light by passing an electric arc through a mixture of gases contained in an arc tube (e.g., argon, mercury, and metal halides). The argon is readily ionized, and enables striking the arc across the lamp electrodes when voltage is applied to the lamp. The heat generated by the arc in turn vaporizes the mercury and metal halides, which produces light as the temperature and pressure increases. The halides generally control the color and intensity of the light produced.
One barrier to the more widespread use of metal halide lamps, and particularly in dimming applications, is an undesirable change in color coordinates, or chromaticity, as the operating power is reduced. Generally, a constant chromaticity is desired for most lighting applications, although certain drift directions may be tolerable. For example, a lamp which dims towards a warmer appearance may be acceptable, such as towards pink-red or towards a lower correlated color temperature (CCT). However, other applications can be intolerant of chromaticity drift.
The current solution to this problem is to simply not use metal halide lamps in dimming applications that are intolerant of chromaticity drift. This of course limits the available opportunities to exploit the various benefits associated with metal halide lamps (e.g., high intensity with good efficiency, etc).